With the progress of science and technology and rapid development of communications and other related technologies, mobile devices, such as mobile phones, PAD, etc. have been integrated into people's daily lives and become an indispensable part thereof.
Due to the characteristics of existing software applications, a lot of storage spaces in a mobile device are often occupied by useless data, resulting in an insufficient storage space in a mobile device, thereby affecting the normal application. For example, a lot of network junk files are often cached in a mobile device, when too many junk files are cached, the start of normal application in the mobile device will be affected. However, network junk picture files account for the majority of the cached network junk files, therefore, in order to delete network picture files, it is inevitable to identify the junk pictures first, thereby how to identify the cached junk picture files effectively becomes an urgent problem to be solved.